This invention relates to a turbocharger bearing arranged in a bearing case for radially mounting a shaft, said bearing comprising a sleeve which is floatingly disposed in a bore in said bearing case and is secured against axial displacement, and an element disposed in the bearing case for securing the sleeve against rotation.
A turbocharger bearing is disclosed in U.S. Pat. No. 4,838,711. To hold the sleeve against rotation, a spring is provided having a first end which engages an axial groove in the sleeve. The bearing case contains a recess opening preferably radially toward the shaft, in which the other end of the spring engages. Between the first end of the spring and the groove a practically linear contact is present due to which comparatively high surface pressures can arise and, in some cases, damage to the sleeve can occur. The spring is disposed substantially in a radial plane with respect to the shaft, while the two ends are bent axially by about 90.degree. each. Especially at the bends there is a special danger of breakage. That is, high-frequency vibration of the spring is to be expected, in which case difficulties must be expected with regard to its behavior under vibration and its life at rotational speeds above 150,000 rpm. Such high rotational speeds are required especially of so-called small turbochargers which are used in engines of up to about 1.5 liters or no more than 2 liters. The shafts of such turbochargers are extremely thin to keep friction losses low, and hence they are flexible. Additional difficulties arise in high-speed turbochargers of this kind due to an effect known as "oil whip," which can occur in speed ranges above twice the first or second critical speed. This effect causes an excitation of the shaft in the sense that the shaft ends perform a superimposed, second rotational movement about the geometric axis. The shaft portion situated between the two axially spaced bearing surfaces of the bearing sleeves is deflected in the opposite direction, and one speaks therefore of a so-called "jump-rope" effect. If the superimposed rotational movement occurs at half the shaft speed, a metal-to-metal contact can occur between the shaft and the bearing sleeve which can result in the complete loss of the bearing's capacity and the destruction of the bearing. The deformation of the shaft can lead to an unacceptable edge pressure between the ends of the sleeve and the journal boxes. Floating journal boxes can perform slight radial and rocking movements independently of one another.
A turbocharger is disclosed in Canadian Patent No. 718,715 with a bearing sleeve having teeth at one axial end. A thrust washer with teeth is connected with the bearing box, and the teeth engage the teeth of the bearing sleeve to prevent rotation. The free movement of the bearing sleeve is at least limited in other degrees of freedom. Thus the other two rotational degrees of freedom, namely about the axes perpendicular to the longitudinal axis, as well as the translational degrees of freedom in the direction of the longitudinal axis, are appreciably limited. A high surface pressure at the contact surfaces between the teeth of the bearing sleeve and of the thrust washer is unavoidable. Due to friction corrosion there is the danger of the destruction of the teeth, and this danger increases with the rotational speed. The free movement or floating arrangement of the sleeve is not realized in a satisfactory manner. The turbocharger of the prior art is designed for rotational speeds up to 80,000 rpm.
The main catalog of Seeger-Orbis GmbH, Wiesbadener Str. 243, D-6240 Koenigstein/Taunus, February 1987, lists retaining rings with tongue-like extensions. These extensions contain holes into which points of appropriately configured pliers are introduced for assembly or disassembly. Such retaining rings serve to axially retain bearing rings, gears and other machine parts on a shaft and/or within a bore. Anti-rotational locking is not easily possible with such retaining rings.
Small turbochargers which rotate at very high speeds, namely over 150,000 rpm, have quite small rotating masses with minimal shaft diameters. The unbalanced stress due to shaft deformation can amount to a hundred times the mass of the rotor. Such shaft flexure and the resulting jump-rope effect may become unacceptably large, so that not only can the above-mentioned mechanical damage occur, but a large amount of noise must be expected. With the spring mentioned in the beginning, the cited problems can be solved in part, while rocking of the sleeve in the bearing bore can result due to the merely one-sided support offered by the bent end of the spring. Due to such rocking, the oil-film cushioning between the sleeve and the bearing bore may be destroyed, or a metal-to-metal contact may even occur between the sleeve and the bearing bore. Due to the linear contact of the spring in the notch in the sleeve and with the other end in the recess in the bearing case, relatively great wear must be expected. Such wear can hardly be prevented even by the lubricant present in the bearing case, primarily due to the linear contact.